In gas turbines with axial flow such as aircraft engines, guide blades and moving blades are usually situated in alternation one after the other in a housing in the compressor and turbine stages. Moving blades form the moving and rotating part of the gas turbine via which the flowing operating medium is either compressed or depressurized. With the aid of guide blades, the flow created by the moving blades may be forwarded in a defined manner. Guide blades for gas turbines usually include, in addition to a turbine blade, at least one radially outer shroud, which is situated on the turbine blade of the guide blade and forms an aerodynamic flow path limitation for the operating medium of the gas turbine in the area of the housing wall. The radially outer shroud has a surface area running essentially perpendicularly to the surface of the turbine blade. On the side of the shroud facing away from the aerodynamic flow path, guide blades often include shroud holding devices with the aid of which the guide blades are secured on the housing in the area of their radially outer shroud.
The fact that targeted gas admission to sections of the housing not situated directly in the flow path of the operating medium is comparatively difficult to accomplish during operation of the gas turbine may be regarded as a disadvantage of the known gas turbines.